Endovascular cryotreatment catheter

ABSTRACT

An elongated catheter device with a distal balloon assembly is adapted for endovascular insertion. Coolant injected through the device may, in different embodiments, directly cool tissue contacting the balloon, or may cool a separate internal chamber. Plural balloons may be provided, wherein a secondary outer balloon surrounds a primary inner balloon, the primary balloon being filled with coolant and acting as the cooling chamber, the secondary balloon being coupled to a vacuum return lumen to serve as a robust leak containment device and thermal insulator around the cooling chamber. One or more sensors may be disposed between the balloons or the vacuum return lumen, to detect leaks and control the flow of fluid through the device. Examples of sensors include pressure and temperature sensors, optical sensors, magnetic flow switches and flow meters.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of application Ser. No. 10/887,271,filed Jul. 8, 2004, entitled ENDOVASCULAR CRYOTREATMENT CATHETER, whichis a Continuation-in-Part of application Ser. No. 09/945,319, filed Aug.31, 2001, now issued U.S. Pat. No. 6,575,966, entitled ENDOVASCULARCRYOTREATMENT CATHETER, which is a Continuation-in-Part of applicationSer. No. 09/378,972, filed Aug. 23, 1999, now issued U.S. Pat. No.6,283,959, entitled ENDOVASCULAR CRYOTREATMENT CATHETER, the entirety ofall of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention relates to endovascular catheters, and inparticular, to catheters for cryotreatment of tissue.

BACKGROUND OF THE INVENTION

The present invention relates to endovascular cryocatheters, such asangioplasty balloons having a freezing function for treating tissue byextreme cooling contact. These catheters have an elongated body throughwhich a cooling fluid circulates to a tip portion which is adapted tocontact and cool tissue. Such a device may include a steering assemblysuch as an inextensible pull wire and a flexible tip to which the pullwire attaches which may be bent into a curved configuration to aid itsnavigation through blood vessels to a desired treatment site. When usedfor angioplasty or the destruction of tissue on the inner wall of avessel, the catheter generally also has one or more inflatable balloonportions which may serve two functions of displacing blood from thetreatment site to allow more effective cooling, and physicallydistending the affected vessel to break up accumulations of plaque.

Endovascular catheters must be of relatively small diameter, andconfigured for insertion along relatively confined pathways to reach anintended ablation site. As such, the cooling fluid must circulatethrough a relatively long and thin body yet apply significant coolingpower in their distal tip. The requirement that coolant be localized inits activity poses constraints on a working device. For example, whenthe catheter must chill tissue to below freezing, the coolant itselfmust obtain a lower temperature to offset the conductive warming effectsof adjacent regions of body tissue. Furthermore, the rate of cooling islimited by the ability to circulate a sufficient mass flow of coolantthrough the active contact region. Since it is a matter of some concernthat proximal, adjacent or unintended tissue sites should not be exposedto harmful cryogenic conditions the flowing coolant must be exposed in alimited region. One approach to cooling uses a phase change refrigerantwhich is provided through the body of the catheter at relatively normalor ambient temperature and attains cooling only upon expansion withinthe tip region. One such device treats or achieves a relatively highrate of heat transfer by using a phase change coolant which is pumped asa high pressure liquid to the tip of the catheter and undergoes itsphase change expanding to a gas in a small chamber located at the tip.The wall of the chamber contacts the adjacent tissue directly to effectconductive cooling or ablation treatment. Other cryocatheters may employgas at high pressure, and achieve cooling via the Joule-Thomson effectat a spray nozzle in a cooling chamber at the distal end of thecatheter.

In an endovascular catheter as described above, a relatively highcooling power may be obtained. However, the expansion of a phase changeor high pressure coolant exiting from a nozzle within a small cathetertip creates highly turbulent flow conditions. The cooling region of thetip may be implemented as a fairly rigid chamber having highly thermallyconductive wall or section of its wall formed for example by a metalshell. However, if one were to replace such a tip with an inflatableballoon as is commonly used for angioplasty, the size of the chamberwould vary considerably as the balloon is inflated, causing substantialvariations in flow conditions of the fluid entering the tip andsubstantial changes in heat transport across the expanding balloon wall.Both of these factors would result in variations of the cooling powerover the tip. Furthermore, coolant materials suitable for high pressureor phase change refrigeration may pose risks when used within a bloodvessel. Accordingly, there is a need for an improved catheterconstruction for cryogenic angioplasty.

Another factor which adds complexity to the task of cryocatheter designis that the primary mechanism of treatment involves thermal conductionbetween the catheter and a targeted region of tissue. Thus, not only isthe absolute cooling capacity of the catheter important, but the natureand extent of contact between the cooled region of the catheter and theadjacent tissue is important. Effective contact may require moving,positioning, anchoring and other mechanisms for positioning, stabilizingand changing the conformation of the cooled portion of the catheter.Slight changes in orientation may greatly alter the cooling range orcharacteristics of the catheter, so that even when the changes arepredictable or measurable, it may become necessary to providepositioning mechanisms of high stability or accuracy to assure adequatetreatment at the designated sites. Furthermore, it is preferable that avessel be occluded to prevent warming by blood flow during treatment.Beyond that, one must assure that the cooling activity is effective atthe surface of the catheter, and further that defects do not cause toxicrelease of coolant or dangerous release of pressure into the body.

Secondary environmental factors, such as the circulation of blood nearor at the treatment site may also exert a large influence on the rate atwhich therapeutic cooling accrues in the targeted tissue.

There is therefore a need for improved catheter constructions to occludeblood flow and form a dependable thermal contact with a vessel wall.

Additionally, the operation of such a device for therapeutic purposesrequires that the coolant be contained within the catheter at all times,lest a leak of coolant enter the body and thereby cause significantharm. Known catheters which employ inflatable balloons often inflate theballoons to relatively high pressures, that exceed the ambient pressurein a blood vessel or body lumen. However, to contain the coolant, thesecatheters generally employ thicker balloons, mechanically rigid coolingchambers, and other similar unitary construction containment mechanisms.These techniques however, lack robustness, in that if the unitaryballoon, cooling chamber, or other form of containment develops a crack,leak, rupture, or other critical structural integrity failure, coolantmay quickly flow out of the catheter.

There is therefore, for security purposes, a need for improvedcryocatheter constructions to robustly contain coolant flow whencryotreatment is performed.

Finally, a major challenge for effective cryotreatment is the ability tofine tune the pressure and temperature of the coolant flow at the distaltip of the catheter, so as to controllably apply cooling to adjacenttissue. The cooling power of the device, created through theJoule-Thomson effect and phase change of the coolant as described above,is generally inversely proportional to the resultant coolant pressureachieved after injection into, and during flow through, the coolingchamber or balloon. Thus, in order to maintain the balloon pressure atsafe levels, without exceeding ambient body pressures, the device mustbe operated at relatively lower balloon pressures, which have theundesired effect of raising the cooling power to levels which aredifficult to control and may even harm or damage the target tissue.Therefore, the enhanced cooling power of the device achieved under suchrelatively low operating pressures must be mitigated by providing someform of tunable thermal resistance between the coolant flow and thetarget tissue.

It is desirable therefore, to provide for an improved catheter systemwhich may safely operate at low balloon pressures while thermallyinsulating the target tissue from excessive cooling.

SUMMARY OF THE INVENTION

The present invention advantageously provides a catheter including aproximal end portion and a distal end portion, the proximal end portiondefining at least one fluid inlet port and at least one fluid outletport. The catheter includes a first expandable membrane and a secondexpandable membrane, the first expandable membrane defining a coolingchamber, the second expandable membrane being disposed around the firstexpandable membrane to define an interstitial space therebetween. Thecatheter includes a coolant injection lumen in fluid communication withthe at least one fluid inlet port and the cooling chamber, and a primarycoolant return lumen in fluid communication with the at least one fluidoutlet port and the cooling chamber. The coolant injection tube, thecooling chamber, and the primary coolant return lumen define a firstfluid pathway. The catheter further includes a secondary coolant returnlumen in fluid communication with the at least one fluid outlet port andthe interstitial space. The interstitial space and the secondary coolantreturn lumen define a second fluid pathway. At least one sensor isdisposed in the second fluid pathway.

In another embodiment of the present invention, a catheter system isprovided, including a coolant supply and a source of vacuum, and acatheter having a proximal end portion and a distal end portion. Theproximal end portion defines at least one fluid outlet port coupled tothe source of vacuum. The catheter includes a first expandable memberand a second expandable member, the first expandable member beingexpandable to define a cooling chamber therein. The second expandablemember is disposed around the first expandable member to define aninterstitial space between the first and second members. The coolingchamber is in fluid communication with the coolant supply. The catheterfurther includes a coolant return lumen fluidly connecting the at leastone fluid outlet port and the interstitial space, the coolant returnlumen being in fluid communication with the source of vacuum. Theinterstitial space and the secondary coolant return lumen define a fluidpathway that is isolated from the cooling chamber. At least one sensoris disposed in the fluid pathway.

In still another embodiment of the present invention, a catheter leakdetection system is provided, including a catheter having proximal anddistal end portions, the proximal end portion defining at least onefluid outlet port coupled to a source of vacuum. An expandable coolingchamber is disposed on the distal end portion and an expandable membraneis disposed around the cooling chamber to define an interstitial spacetherebetween, the cooling chamber being in fluid communication with acoolant supply. A coolant return lumen fluidly connects the at least onefluid outlet port and the interstitial space, the coolant return lumenbeing in fluid communication with the source of vacuum. The interstitialspace and the secondary coolant return lumen define a fluid pathwayisolated from the cooling chamber. At least one sensor is disposed inthe fluid pathway and detects the flow of fluid in the fluid pathway.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 illustrates a balloon catheter system in accordance with a firstembodiment of one aspect of the present invention;

FIG. 2 shows a cross section taken along the axial direction through theballoon portion of another embodiment of the invention;

FIGS. 3A-3D illustrate four embodiments of thermally conductive balloonsin accordance with the invention;

FIG. 4 illustrates another embodiment of the invention;

FIG. 5 illustrates balloon orientation;

FIG. 6 illustrates an embodiment with proximal anchoring/occlusionballoon;

FIG. 7 illustrates another two balloon cryocatheter;

FIG. 7A illustrates a section through a multilumen catheter suitable forthe practice of the invention;

FIGS. 8A and 8B show another balloon embodiment of the invention in itsdeflated and inflated state, respectively;

FIGS. 9A and 9B show a balloon embodiment with separate cooling andinflation media;

FIGS. 10A-10B show yet another balloon embodiment;

FIG. 1C illustrates a further variation on the embodiment of FIGS.10A-10B;

FIG. 11 illustrates another embodiment;

FIGS. 12A and 12B illustrate delivery embodiments;

FIG. 13 shows a cross section taken along the axial direction of a dualballoon catheter system;

FIG. 13A illustrates a transverse cross-section of the catheter bodyalong lines A-A in FIG. 13;

FIG. 14 illustrates a cross section taken along the axial directionthrough the distal portion of the catheter system of FIG. 13;

FIG. 15 illustrates the catheter system of FIG. 14, when the outerballoon is under vacuum pressure;

FIGS. 16A, 16B, 16C, 16D, and 16E illustrate various alternativeembodiments of the catheter system of FIG. 14; and

FIG. 17 shows the catheter system of FIG. 14 with a pressure transducerlocated in the inner balloon.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a treatment catheter 10 in accordance with a basicembodiment of the present invention. Catheter 10 includes a handle 10 a,an elongated intermediate body portion 10 b, and a distal end 10 c. Aninextensible guide wire 21 extends from the handle to the tip 10 c forexerting tension via a take up wheel 22 that is turned by lever 24 tocurve the tip of the catheter and steer it through various branch pointsalong the route through a vessel to the intended treatment site.Alternatively, the catheter may be provided with a central guide wirelumen. In that case, a guide wire is inserted into the vessel up to orpast the treatment site and the catheter is then placed over the guidewire. As further shown in FIG. 1, a balloon 30 is attached to the distalend of the catheter and as described further below is in communicationvia the intermediate body 10 b and handle 10 a with an inlet 40 a forthe refrigerant fluid, and an outlet 40 b through which spentrefrigerant returns. The handle may also receive electrical connectionsvia a port or cable 45 for various sensing or control functionsdescribed further below.

General principles concerning the construction or operation of such acryocatheter may be found in U.S. Pat. No. 5,281,215, which isincorporated herein by reference for purposes of disclosure andillustration.

In accordance with one aspect of the present invention, the refrigerantfluid applied at the port 40 a is applied through a first passage to theballoon and returned from the balloon through a second passage to theoutlet 40 b, at a positive pressure. For example, a valve may be presentdownstream of the balloon to set a back pressure which effects inflationof the balloon by the coolant fluid. As illustrated in FIG. 1, the valvemay be implemented by a check valve 51 positioned at the port 40 b andset for example to open at a pressure of 10 psig to maintain asufficient back pressure in the return line for inflation of the balloon30. In alternative embodiments, the check valve 51 may be replaced by acontrollable valve, or a pressure sensing arrangement that provides afeedback signal in conjunction with an electrically controlled valve, toassure that the desired inflation pressure is achieved at the balloon 30while allowing return of coolant continuously through the outlet 40 b toa control console. In either case, the return valve maintains a minimumpressure at the outlet side of the catheter assembly. This minimumpressure is at a level higher than blood pressure to assure that theballoon inflates and occludes the vessel in which it is located.

In one embodiment, a relatively thin balloon is placed at the end of thecatheter and is folded over the shaft so that when the coolant fluid isinjected, the balloon opens and inflates to occlude blood flow withinthe vessel where it is situated. By increasing the injection pressure tothe balloon, the rate of cooling is increased to apply cryogenicconditions at the surrounding wall of the vessel. Preferably, arefrigerant such as liquid CO2 is employed having relativelycontrollable thermal characteristics for the desired treatment range.Leakage of CO2 into the blood stream, if it occurs, is harmless in smallamounts. This construction may be varied somewhat. For example, theballoon may be a relatively thick-walled balloon intended when inflatedto exert mechanical force against the vessel wall to break up plaque. Inthat case, relatively higher inflation pressures are used, and theoutlet valve 51 may be operated to maintain back pressures up to severalatmospheres or more. Furthermore, it will be understood that therelatively small cross-sectioned opening present in the body 10 d of thecatheter may itself operate to cause a pressure drop, or back pressure,so that the valve 51 may be set to a lower opening pressure threshold,so long as back pressure at the balloon is maintained sufficiently highin the range for balloon inflation.

In accordance with one aspect of the present invention, the balloonoperates to treat adjacent vascular tissue by freezing.

This is achieved in one preferred aspect of the invention by a balloonfabricated with a wall metallization that enhances the heat transferrate through all or a portion or pattern of the balloon wall. FIG. 2 isa cross-sectional view through one such balloon 60 taken in a planealong the axis of the device. As shown, the balloon 60 is attached tothe end of the catheter shaft 10 b and has a refrigerant injection tube4 extending to its interior so that refrigerant flows out the end orother apertures which are provided in the distal portion of the tube 4and fills a chamber 62 defined by the interior of the balloon. A guidewire lumen 6 may extend to the distal tip for facilitating insertion,and a steering wire (not shown) may be positioned in the adjacentportion of the tip or extend through the balloon, in a manner generallyknown in the art of catheter design to deflect the tip portion. Withinthe body of the catheter shaft 10 b, the region of the lumen notoccupied by the injection tube and other described components serves asa return passage for the refrigerant released from the nozzle end 1 ofthe injection tube 4. As further shown in FIG. 2, the balloon 60 has awall of membrane thickness with a pattern of metallization, visible asmetal regions 64 a, 64 b . . . 64 c disposed over its surface. Thepatterned metallization regions 64 have higher thermal conductivity thanthe bulk balloon membrane material, and define regions at whichdestructive freezing contact to the vessel wall itself will occur whenthe balloon is inflated.

FIGS. 3A through 3D illustrate various patterns suitable for use in thepresent invention in perspective view on a representative balloon 60. Asshown in FIG. 3A, one such pattern includes a plurality of substantiallyaxially oriented lines 71 disposed around the circumference of theballoon. The balloon is shown in a partially inflated posture. Wheninflated more fully, the balloon expands and the lines 71 move apartaround the circumference. Since expansion occurs only in the radialdirection, the metal does not constrain expansion of the balloon orintroduce localized stresses or cracking during expansion.

FIG. 3B shows a second useful pattern in which the conductive patterninclude a zigzag or meandering arrangement of conductive metal portions72 configured such that bends or junctions of successive path regionallow the balloon to expand without constraint. In this case, radialenlargement and circumferential expansion of the balloon wall simplybends the metal paths. In general, any of the shapes which have beenfound suitable for expanding metal mesh, wire or coil stents may beuseful as surface patterns for the balloon membrane to enable it toundergo radial expansion without introducing mechanical faults into theballoon membrane.

The invention also contemplates conductive patterns in which theconductive regions consist of a plurality of substantially separated ordisjoint small loci. These may consist of solid regions such as dots 73,or squares or rectangles of relatively small overall extent, e.g., underseveral millimeters across, to produce dimpled regions of conductionextending over the whole surface of the balloon as shown in FIG. 3C, ormay include one or more large areas so as to adapt the balloon forapplying a particular pattern of localized cooling, such as a coolingthrough on side of the balloon while still allowing the balloon toexpand in its entirety to firmly lodge the balloon within the vessel anddisplace blood so as to allow the cooling surface of the balloon toeffectively and directly contact the vessel wall.

FIG. 3D shows another useful pattern 74 for the balloon.

The metal or conductive regions 71, 72, 73 and 74 may be applied usinglithographic printing technology, for example, by applying ametal-loaded thermally conductive ink in a polymer base to the membrane,or by applying complete coatings and patterning and etching away regionsby lithography techniques to form the desired pattern. Such patterns mayalso be formed by applying a metal foil layer or depositing such a layerby plating or sputter deposition techniques and employing lithographicmethods to pattern the continuous layers. In general the pattern isformed so as to create a desired pattern of icing lines for effectivelydestroying tissue at the patterned areas of conductive contact when theballoon is inflated. The conductive regions 64, 71-74 may also becreated by adding thermally conductive materials such as copper powder,flakes or fibers to the material of the balloon membrane itself. In thatcase the powders or fibers are preferably mixed with the appropriateelastomer or polymer material from which the balloon is to be formed,and the balloon is then formed by a known technique such as molding,forming on a mandrel, dipping or other common balloon forming technique.When patterning is desired, a standard elastomer and a conductivelyloaded elastomer may be painted on in bands or otherwise patternedduring the manufacturing process to create the desired thermal contactregions.

FIG. 4 illustrates another embodiment 80 of the present invention. Thisembodiment has a multi-balloon structure and a cooling segment 84 at thecatheter tip. As illustrated, segment 84 corresponds to the expansionchamber or region of greatest cooling activity of the catheter andincludes a cooling pattern assembly. This may be a spiral metal wrappingthat provides stiffness, form and thermal conductivity to the segment. Afirst balloon 82 is positioned on one side of the cooling segment 84 toserve as an anchor and blood vessel occluder or flow blocker, and inthis embodiment a second balloon 86 extends from the other end of thecooling segment. As shown, the first balloon is substantially ovaloidand symmetrical, while the second balloon 86 has a tapered, trumpet- orbell-shaped aspect that allows it to wedge at the end of a vessel, forexample, in the ostium or junction of the vessel end to an organ. Thus,while the balloon 82 is inflatable within a vessel to serve as ananchor, balloon 86 is adaptable to fit in an opening and occlude theopening, or define an end-contact geometry for positioning the coolingsegment 84 in close proximity to the vessel end opening.

It will be appreciated that the cooling segment 84 in this embodimenthas a relatively fixed diameter and is not subject to inflation. Ratherit has high thermal conductivity and in use when actuated by flow ofrefrigerant within the catheter, an ice ball forms to extend its thermalrange. The region of ice formation is indicated schematically by theexternal dotted profile positioned around the cooling segment of thecatheter.

As further shown in FIG. 4, the catheter assembly may include a guidewire lumen 87 for over-the-wire insertion, or for monorail guidingmovement of the distal tip. Alternatively, the distal termination mayinclude a conventional wiggler tip or a steering assembly manipulatedfrom the handle end of the catheter. Furthermore, the positions of theballoons 82 and 86 may be interchanged, with the anchor balloon 82 beingpositioned distal to the cooling segment 84 and the tapered or trumpetballoon 86 positioned proximally thereof. This configuration allows useof the catheter by insertion along the opposite direction of the vessel,for example, through a cardiac chamber and into a vessel exiting thechamber.

Thus, in accordance with this aspect of the invention, the cryocatheterincludes a cooling segment that is positioned and anchored by one ormore occlusion balloons. Preferably at least one of these balloons isinflated with the carbon dioxide or other biocompatible refrigerant fromthe cooling segment. The balloons are not necessarily of equivalentdimension, geometry or compliance. The anchoring balloon may be inflatedvia an individual inflation lumen, thus allowing the position to beprecisely set and this balloon inflated before cooling is initiated. Thetapered balloon may be inflated in multiple ways depending on thedesired effect. For example, when it is desired to treat a lesion in avessel in close proximity to the ostium, for example, in the renalarteries, the catheter may be configured such that the coolant bothinflates and cools the balloon 86, so that its tapered surface is acontact cooling surface for treating the adjacent vessel tissue.

In another embodiment, an individual inflation lumen may be provided forthe flared balloon 86. In that case, this balloon may be inflated firstwhen it is desired, for example, to place the cooling segment 84 inclose proximity to the ostium. Balloon 86 may then serve the functionboth of positioning the cooling segment, and of occluding blood flow inthe treated region. Thus, the catheter of FIG. 4 may be used forcryogenic treatment in a blood vessel and is well adapted to forminglesions near or at the ostium of the vessel. As noted above, byreversing the positions of balloons 82 and 86, the catheter may benavigated from the opposite direction along a vessel to treat a sitenear a junction. Furthermore, by reversing the taper orientation of theballoon 86, the catheter may be configured to more effectively treat ajunction of particular size and accessible from one orientation.

In yet another embodiment, the catheter is manufactured without thesymmetric anchoring balloon 82 and carries only the cooling segment 84and trumpet balloon 86 at its tip, forming a configuration for makingrelatively linear lesions in locations where the vessel diameter changesrapidly. For example, such a modified catheter may be used for treatmentin an antegrade approach to a treatment site along the femoral artery,as shown in FIG. 5.

FIG. 6 shows another embodiment of the invention. This embodiment issimilar to that of FIG. 1, but the catheter tip is configured so thatrather than applying cryogenic cooling through an expandable balloon,the cooling segment is of substantially fixed diameter, which may becomparable to that of the catheter body, and it extends distally from aproximal balloon which functions to occlude the blood vessel in whichthe catheter lies. As shown, the tip portion is deflectable by means ofa tension wire connected to the handle, so as to more effectivelynavigate along vascular branching passages. The tension wire may also beoperated to urge the cooling segment into contact at the intended targetsite. As in the embodiment of FIG. 1, the coolant is preferably liquidcarbon dioxide, and the coolant return line is kept at a pressure higherthan the nominal blood pressure in the vessel being treated. The balloonmay thus communicate with the return flow of gas so that the returningcoolant inflates the balloon and effectively occludes the vessel. Byplacing the balloon sufficiently far downstream from the cooling segmentor liquid expansion opening, the return gas may be warmed sufficientlyto avoid freezing tissue in the balloon occlusion region. Similarly, bylocating the balloon closer to the freezing segment, the cooler carbondioxide will provide cryogenic treatment through the balloon surface toan additional region of tissue adjacent the cooling segment. In furtherembodiments, a distal balloon (not shown) may also be provided. Alimiting orifice is preferably placed in the catheter lumen between thecoolant injection tube and the distal balloon to prevent cold gas fromentering the balloon too rapidly. Thus, the distal balloon istrickle-filled from the expansion region of the catheter to providedependable occlusion or anchoring without damaging surrounding tissue.

In any of the foregoing embodiments, applicant contemplates that a valverelease, or an actively-switched vacuum connection may be provided toquickly deflate the balloons on demand by reducing back pressure of thereturn lumen in the catheter body.

FIG. 7 shows another embodiment 90 of the invention, illustrated by wayof an axial cross-section taken in a diametral plane through the tip ofthe catheter. As shown, the tip of the catheter includes a pair ofballoons 92 a, 92 b surrounding a cooling segment 93. As shown, thecooling segment and balloons may be formed by a common cylindricalmembrane surrounding the catheter body, while the elongated catheterbody provides necessary lead in and return passages for inflation of theballoons and delivery of cooling fluid. The cooling segment possesses aheat exchanging surface 93 a which may also be a metallic or structuralcomponent of the device. For example, the surface indicated by elements93 a in the Figure may be formed by a metal spring surrounding the body,or by a metal coating or foil lithographically etched to form a coilembedded in or surrounding the membrane. Alternatively, or in addition,the cooling segment may be implemented by a helically slotted coolantsupply tube fixed in the lumen of the catheter shaft to preferentiallydirect the coolant in liquid form against the wall of the coolantsegment. In this embodiment, the catheter shaft 91 is preferably amultilumen shaft, implemented as shown, for example, in FIG. 7A. Thelumena may include, in addition to a guide wire lumen if one isprovided, a lumen 94 for coolant delivery, a larger return lumen 94 cwhich may surround the delivery lumen, and one or more auxiliary lumens94 a, 94 b. In various embodiments the auxiliary lumens are connectedvia the handle to separately inflate one or more of the balloons 92 a,92 b. Alternatively, when balloon inflation is performed by trickleinflation of gas from the cooling segment 93, an auxiliary lumen may beused for a controllable vacuum passage which is actuated to deflate aballoon. As noted above, inflation of the balloons may be effected bythe spent or warmed phase change coolant gas in its course towards thereturn lumen.

When balloon inflation is entirely effected by gas from the coolingsegment, one or more of the lumena may be used to contain a steeringwire or other accessory unrelated to fluid transfer. Thus as illustratedin FIG. 7, the catheter 90 may be configured with a guide wire lumen 95for navigation within a vessel, or may include a steering and supportwire assembly 98 within the catheter body to aid insertion. Theinvention also contemplates that, in a manner similar to the embodimentsdescribed above, the catheter 90 may be implemented with a singleocclusion balloon, which is preferably placed proximal to the coolingsegment for antegrade approaches to lesion treatment. Alternatively, theballoon may be placed distally of the cooling segment when it is desireduse the device for treating lesions by a retrograde approach. When bothocclusion balloons 92 a, 92 b are present, the cooling segment isreadily anchored in short, branched or turning passages by inflating oneor both balloons. The balloons may further be of different sizes or maybe shaped as discussed above for particular applications and vessels.

In addition to the specific embodiments discussed above, in one aspectof the present invention, the invention include a balloon disposed as anannular chamber or cuff around a cooling assembly. Such an embodiment isshown in FIGS. 8A and 8B. In accordance with this aspect of theinvention, the catheter 10 carries a coolant injection tube 1 whichextends to a cooling chamber structure 103 that is surrounded by acooling balloon 112. The cooling chamber structure 103 is relativelystiff or even rigid and has substantially fixed dimensions. It may beimplemented, for example with a cylinder formed of hard polymer or metaland having a fixed diameter. Surrounding the cooling chamber cylinder103 is a balloon 112 shown in its deflated state in FIG. 8A and shownfully inflated in FIG. 8B. When the cooling and balloon inflation arecarried out by the same medium, the cooling chamber 103 may beimplemented with a perforated chamber wall. The use of a substantiallyrigid chamber 103 allows the coolant flow upon exiting the injectiontube to undergo substantially regular conditions and therefore provideswell regulated and predictable cooling characteristics. However, theinvention also contemplates that the balloon may be inflated with apressurizing medium other than that provided by the refrigerant. Ineither case the balloon may be formed of a quite thin membrane, on theorder of 0.02 millimeters thickness or less, so that in this case itpresents very little impediment to heat conduction.

In this construction, the balloon serves as a compliance member toconform to irregular tissue surfaces, and may be used to apply pressureto a lumen to enlarge the lumen in a manner similar to that employed incoronary angioplasty and fallopian tuboplasty procedures. The balloonmay also be operated to occlude blood flow when used in an endovascularcatheter for rapid therapy since the inflation portion may be deployedor deflated substantially instantaneously. The balloon further operatesto center the cooling chamber within the lumen, thus assuringsubstantially concentric cooling characteristics for the treatment.Finally, the balloon serves to anchor the cooling chamber in position.

The provision of a fixed dimension cooling chamber surrounded by anannular balloon that is inflated by a separate medium, advantageouslyprovides an enhanced spectrum of operating characteristics. Severalexamples follow illustrating the range of this construction of theinvention.

FIGS. 9A and 9B schematically illustrate the construction of a guidewire cryocatheter 200 having such a circumferential cushioning balloon212. This construction may also be applied to cooling other cylindricaltissue structures or body lumens, including organs or structures such asthe fallopian tube, esophagus, biliary duct, ureter, gastrointestinaltract and the bronchus. For each of these different applications, therelative diameter of the cooling chamber and the thickness of balloonportion may be varied so as to achieve for example high total coolingwith a large cooling chamber and an effective rate of heat transfer fromthe surrounding tissue area through a relatively thinner layer ofcooling balloon. Notably, the balloon may inflated with a medium such asprecooled saline solution having a high rate of thermal conductivity anda high thermal storage capacity, to achieve quick chilling and tomaintain a stable thermal set point without having to design the coolingchamber to bear the full thermal load alone.

As shown in FIG. 9A, the injection tube 201 enters the expansion chamber203 and injects refrigerant at high pressure, which then expands in thechamber and is exhausted through the exhaust lumen 205 which constitutesthe major portion of the catheter shaft. The balloon 212, shown in itscollapsed state in FIG. 9A around the circumference of the coolingchamber, is inflated via a balloon inflation lumen 208. Applicantcontemplates that the balloon inflation may be effected by a number ofinflation media, including a gaseous coolant medium from the other(coolant) chamber 203. However, preferably, in this embodiment anincompressible liquid such as saline solution having a high thermalcapacity and excellent heat conductive properties is applied through theinflation tube 208 to fill the balloon as shown in FIG. 9B. The externalsurface of the expansion chamber 203 may be provided with texture, suchas a plurality of isolated bumps or dimples 207, of which several areshown in cross-section, to provide unobstructed fluid percolationpassages along the surface and assure that the balloon inflation fluidmay have free access and flow quickly to and from the passage 208. Thisallows the balloon to fully deflate when fluid is withdrawn via passage208.

A guide wire lumen 220 passes centrally through the cooling chamberassembly and as shown in FIG. 9B accommodates a guide wire 221 fordirecting and positioning the catheter. As further shown in thoseFigures, the outer diameter of the cooling chamber may extend for arelatively great portion of the total diameter of the device so that theballoon portion occupies only a thin shell which effectively extends thereach of the cooling chamber and provides a short heat conduction pathtogether with firm compliant contact with surrounding tissue. As notedabove, when used for angioplasty and other cryogenic treatment contextsthe balloon serves to apply a stretching or extensile force to tissue,which is conducive to the desired tissue treatment destruction orregeneration process. The provision of such enlarged cooling chamberalso provides a greater external surface area for the coldest centralstructure of the catheter, greatly enhancing the rate of thermaltransfer achieved with the balloon assembly.

In general the body of the catheter may be comparable to that ofexisting treatment devices, e.g., one to four centimeters in length foran endovascular angioplasty device. However the cryogenic portion neednot extend the full length of the tip assembly, and the structure mayinclude axial extension portions which are not cryogenically cooled.

FIGS. 10A through 10C illustrate a construction of a cryocatheter 300 ofthis type. In this embodiment, the tip of the catheter includes chambers303, 303 a and 303 b all located within the balloon. The chamber 303serves as a cooling expansion chamber in the manner described above, andthe cooling injection tube 301 opens into that chamber. At the proximaland distal ends of chamber 303, pair of dummy chambers 303 a, 303 bextend continuously with the main body of the chamber to form a singleelongated cylindrical structure lying within the balloon 312. However,the end chambers 303 a, 303 b are isolated from the injected coolant,and themselves form dummy spaces or uncooled regions that serve simplyto provide positioning support. As further shown in FIG. 10A, theballoon 312 has corresponding segments denoted 312 a, 312 b and 312 cthat are partitioned from each other such that the end segments areseparated from the central cooling portion of the balloon. Thesesegments lie over subchambers 303 a, 303 and 303 b. They may be seriallyconnected or separately supplied with inflation material, so fluidentering the balloons is cooled only in the central region.

The illustrated embodiment of FIG. 10A has a generally continuousballoon contour in which at least a portion of the end segments 312 a,312 b inflates to the diameter of the surrounding blood vessel or tissuelumen and serves to displace blood, fluid or tissue away from thecryogenic treatment portion at the center of the catheter tip. As shownin FIG. 10B, this has the effect of creating a cooling region that formsa relatively symmetrical ice ball volume (indicated by dashed lines inthe Figure) around the vessel and catheter tip, with greater depth ofpenetration centered directly over the cryogenic chamber and withcooling damage tapering off away from that region. The balloon need notbe a single continuous or partitioned balloon but may be implementedwith separate balloons that in turn may be inflated via separate filleror inflation tubes (not illustrated) so as to more effectively achieveor more independently initiate the blocking and heat isolationfunctions. FIG. 10C illustrates one such embodiment 400, in which acryogenic balloon 412 is surrounded by first and second blocking orblood displacing balloons 412 a, 412 b that are offset a short distanceaway from the ends of the coolant chamber. With this construction theexcluding balloons may be positioned more remotely from the cryogenicsegment.

In any of the foregoing embodiments, the balloon may be configured toapply a chilling level of cold without freezing or destroying tissuewhen appropriate for the tissue involved. As with the basic embodimentshown in FIGS. 8A and 8B, the catheter of the present inventionpreferably allows the withdrawal of sufficient thermal energy from thetarget site to freeze tissue, while the balloon anchors or enhances thepositioning of the cryogenic source within the lumen so as to deploy theresulting ice ball in an appropriate relation to the surrounding tissue.The balloon enhances control of adjacent blood flow and may be used toarrest blood flow in the vessel entirely so that therapeutic coldaccrues more quickly and is not dissipated. By actively pumping out theinflation fluid, collapse of the balloon following therapy allows moreimmediate resumption of circulation to perfuse tissue. Furthermore, byusing a liquid-inflated balloon, the device may be deployed in much thesame manner as an existing angioplasty catheter, and the guide wirelumen allows simple navigation and use of the device without requiringthat the physician or cardiology specialist acquire additional operatingskills or specialized training.

The catheter shaft may accommodate various lumens either as part of theshaft extrusion, or by carrying them as separate tubes such as aninjection tube, a coolant exhaust lumen, a balloon inflation lumen, aguide wire lumen and other lumens, for example, for carrying wires toheating elements and/or monitoring devices to sense pressure,temperature and other sensing functions. By making the diameter of thecryogenic chamber large in relation to the targeted tissue lumen, theballoon may be formed with a low interior volume, facilitating thethawing of the inflation medium and reducing the time of total vascularobstruction. The thawing may further be advanced by providing andactivating one or more heating elements, which may include any of a widevariety of heating means within the catheter body, such as resistiveheating, radio frequency heating, laser heating applied via an opticalfiber extending through the catheter body, microwave heating or heatedgas or liquid infusion applied to the balloon portion. These may alsoinclude, in various treatment regimens, sources of energy that areexternally applied to a catheter designed to preferentially receive suchenergy. Such external heating energy sources may, for example, beultrasound or electromagnetic radiation applicators. The heater may alsoinclude various semiconductor, thin layer resistive or other similartechnologies deployed, for example, on the balloon surface so as to heatone or more of the wall of the body lumen, the balloon inflation medium,or various pieces of the catheter structure.

In addition, the period of blood flow obstruction may be further reducedby providing a structure as shown in FIG. 11. In this case, the catheter500 includes perfusion channels 531, 532 that extend through thecatheter structure to allow blood to flow along the tissue lumen duringthe balloon inflation time interval and before extreme cooling hasoccurred to freeze off the central region. In this embodiment, theballoon may be inflated to securely position and center the assemblywhile blood continues to flow along the vessel. Cooling is then started.While the bypass channels 531, 532 may be expected to freeze off oncethe cooling injection has started, the invention also contemplates thatthe bypass channels may be insulated from the cooling chamber, or theymay include resistive or other heating elements to maintain theirtemperature suitable for continued blood flow during cryoablation. Suchbypass passages may also be positioned in part in or through thecatheter shaft or guide wire lumen.

The invention also contemplates a catheter as described above combinedwith other known catheter subassemblies or accessory devices such asdrug delivery, energy delivery or stent delivery elements, or structuresfor delivering radiation. In other embodiments the catheter may includeone or more additional balloons such as a primary angioplasty balloon inaddition to the blocking balloons and the cryotreatment balloondescribed above. In yet other embodiments of the invention, the cathetermay include a supply tube for ejecting a bioactive or simply thermallyconductive material in the space surrounding the cooling portion, toform a temporary frozen plug which may be left in place followingwithdrawal of the catheter.

FIGS. 12A and 12B illustrate two such delivery catheters 600, 700. Asshown in FIG. 12A, a first delivery catheter 600 includes an elongatedbody and cryogenic tip 610 with a cooling chamber 603 fed by a coolantinjection lumen 601 as described above. Catheter 600 further carries astent 620 on its outer surface and is configured to deliver and installthe stent at an endoluminal site. By way of example the stent 620 isillustrated as having ends 621, 622 contoured to retain the stent on thecatheter during delivery, but other retention means, such as a removableor telescoping retaining sheath may be employed. The stent is made of ashape-memory alloy or other biphasic temperature-dependent material thatchanges its shape when brought to predetermined temperature. Foroperation, the catheter tip is deployed to a desired site and thenoperated to bring about a temperature-dependent change in shape ordimension of the stent 620. This may be accomplished before, during,after, or independently of, the cryogenic treatment of nearby tissue.Depending on the particular alloy employed in stent 620, the fixation inposition and shape change may be effected by applying cryogenictemperature, or else a mild amount of cooling may be applied to causethe stent to retain a compact shape during insertion and the stent maysubsequently deploy as the surrounding temperature rises to normal bodytemperature. It will be understood that in general the alloy propertiesof such materials may be adjusted so that a relatively large change inshape or conformation is achieved at one temperature threshold, whichmay be above or below body temperature. Accordingly, for this aspect ofthe invention, applicant contemplates the possibility of providing aheater as well as the cryochamber 603 to provide both hypo- andhyperthermal conditions to carry out stent deployment.

FIG. 12B illustrates another embodiment 700 of a cryogenic deliverycatheter of the invention. This embodiment again has the basic structureof a cooling chamber 703 in a distal cooling tip 710 fed by a coolantsupply lumen 701. However, in this embodiment an additional fluiddelivery line 725 extends through the catheter body and is mounted todeliver fluid F externally of the tip 710 into the space between thecooling chamber exterior wall and the surrounding tissue. The deliveryline 725 may have one or more outlets positioned to provide fluid F indefined locations. As illustrated in phantom by element 715, aperforated membrane or other external distribution structure may also beprovided to disperse or spread the fluid F exiting the delivery line725. In general, the delivery line 725 may deliver a therapeutictreatment liquid, or simply a heat conduction fluid to cryochambersurface. Applicant contemplates generally that during cryotreatment, thefluid F will freeze in place, forming a plug that blocks flow, conductsthermal energy, and otherwise cooperates with the cryotreatmentoperation as described above. Advantageously, however, upon (or evenprior to) completion of the freezing treatment, the catheter 700 may bewithdrawn while leaving the frozen fluid mass in place. This mass thencontinues to chill the lumenal tissue wall, while (in the case of avessel) circulation is immediately restored through the center. Thus,the duration of catheter freezing operation or the duration of bloodflow occlusion may each be reduced, offering significant clinicaladvantages.

FIG. 13 illustrates yet another embodiment of the present invention, adual balloon catheter system labeled generally as 800. Catheter system800 includes a catheter 805, a handle unit 810, a guidewire port 815, aguidewire tube 820 enclosing a guidewire lumen 822, a coolant port 825,a coolant injection tube 830 enclosing a coolant injection lumen 835, avacuum port 840, a vacuum return tube 845, a primary vacuum return lumen850, a secondary vacuum return lumen 855, an inner balloon 860, an outerballoon 865, a cooling chamber 870, a proximal thermocouple 875, adistal thermocouple 880, and a distal tip 883. The thermocouples mayalso be coupled to a temperature gauge 885 coupled to handle unit 810.

The catheter 805 includes an elongate tube or series of tubes, conduits,flexible or rigid members generally suited for the flow of coolanttherein, and for the insertion of such catheter into narrow body lumenssuch as blood vessels. Each of these tubes, conduits or members mayinclude a number of lumens. As used herein, the term lumen refers notmerely to the bore of a tube, but refers generally to a defined fluidpathway, suitable for the flow of coolant therethrough, connecting twoor more spaces or elements such that the spaces or elements are in fluidcommunication. The catheter 805 is constructed similar to thoseembodiments previously discussed herein, and operates in a similarfashion so as to enable cryotreatment of tissue.

As shown in FIG. 13, the catheter 805 is coupled to a handle unit 810 atits proximal end, and both of balloons 860 and 865 at its distal end.The handle unit 810 is fitted with multiple ports, including a guidewireport 815 for the insertion of a guidewire (not shown) into guidewiretube 820. In addition, the handle unit 810 includes a coolant port 825for the injection of coolant from a coolant supply (not shown) intocoolant injection lumen 835. The coolant injection lumen 835 is disposedbetween the coaxial coolant injection tube 830 disposed around guidewiretube 820, as illustrated in FIG. 13.

A vacuum port 840 is also coupled to the handle unit 810, such portbeing coupled to a suitable vacuum generating device. A vacuum returntube 845 is disposed coaxially around the coolant injection tube 830 andinside of the catheter tube 805. This creates two separate coaxialvacuum return lumens: a primary vacuum return lumen 850 disposed betweencoolant injection tube 830 and vacuum return tube 845, and a secondaryvacuum return lumen 855 disposed between the vacuum return tube 845 andthe catheter body 805.

FIG. 13A illustrates a cross-section taken in the transverse directionof the catheter 805, along lines A-A in FIG. 13, showing the coaxialarrangement of the various tubes and lumens discussed above.

Turning back to FIG. 13, the catheter 805 is coupled at its distal endto two balloons, inner balloon 860, and outer balloon 865. Each of theseballoons include materials and are constructed in a manner similar tothose balloons discussed in previous embodiments. The inner balloon 860has an open proximal end coupled to the coaxial return tube 845, and mayhave its lateral outer surface adhesively coupled to the guidewire tube820. The outer balloon 865 is disposed around the inner balloon 860,having its proximal end coupled to the catheter tube 805 and its distalend coupled to the distal tip 883 disposed around the distal end portionof the guidewire lumen 822.

High pressure coolant is injected through the coolant port 825 into thecoolant injection lumen 835, whereby it flows through such lumen to beinjected into the inner balloon 860. The inner balloon 860 therebyexpands to create a cooling chamber 870 therein. The coolant then flowsout of the cooling chamber 870 into the primary vacuum return lumen 850,and eventually out of the device through the vacuum port 840. Forpurposes of this invention, a “vacuum” is merely the effect of fluidevacuation, wherein static pressure in a space may be below that ofatmospheric, or may be below the static pressure in the flow regionimmediately “upstream” of such space. Therefore, a “vacuum”, as usedherein, may refer simply to the existence of a negative pressuregradient in a flow region. Thus, the flow of coolant from the coolingchamber 870 through the primary vacuum return lumen 850 is driven by thenegative pressure gradient created when the pressure therein is lowerthan the static pressure of coolant in the chamber 870.

While the coolant is flowing through the chamber 870, two thermocouplesdisposed therein may take temperature readings of the coolant, suchtemperature being measured by the temperature gauge 885. While theproximal thermocouple 875 takes a temperature reading in the proximalsection of the cooling chamber 870, a distal thermocouple 880 takes areading of coolant temperature in the distal section of cooling chamber870. As coolant is injected into the inner balloon 860, the flow ofcoolant in such balloon is non-uniform, unsteady, and turbulent, suchthat a uniform temperature profile for cryotreatment is not achieved fora finite time. The thermocouples 875 and 880 provide for feedbackcontrol of the flow of coolant, and of the resultant temperature profileachieved in chamber 870, thereby enabling more efficient cryotreatment.

FIG. 14 illustrates the distal end portion of the catheter system 800 ofFIG. 13. In addition to the elements displayed in FIG. 13, FIG. 14illustrates a coaxial coolant injection orifice 905, an interstitial,“intra-balloon” space 910 disposed between inner balloon 860 and outerballoon 865, and coolant flow lines F. Upon flowing through the coaxialinjection tube 830, coolant enters the chamber 870 through the injectionorifice 905 located in the distal half of inner balloon 860. Coolantthereafter generally flows in the direction F until the inner balloon860 is inflated to form the cooling chamber 870 in substantially theshape and form shown in FIG. 14. Coolant then flows out of the chamber870 through the primary vacuum return lumen 850.

While coolant is contained in the chamber 870, the flow therein isregulated by the use of thermocouples 875 and 880, so as to control thetemperature profile therein. The pressure conditions inside of thechamber 870 may be regulated by controllably injecting the coolantthrough the orifice 905, such that the desired mixture of liquid and gasphase coolant is evaporated and expanded, respectively, inside thechamber to achieve the desired cooling power. The injected coolant maybe (i) substantially in gas phase immediately upon injection, therebyusing mainly Joule-Thomson cooling to lower the temperature profile inthe chamber 870, or, (ii) substantially in liquid form, allowing forbetter control of temperature across the length of chamber 870, whilestill providing cooling through the endothermic boiling of liquid phasecoolant.

In either case, the pressure inside of the chamber 870 must bemaintained at safe levels for insertion of the device into the humanbody. Generally, the static pressure of coolant inside of the chamber870 must be maintained below 15 psia, or only slightly above the ambientpressure outside of the device. If a leak or rupture through the innerballoon 860 develops, the vacuum applied through the secondary vacuumreturn lumen 855 will act to siphon any leaking coolant from space 910into the vacuum return lumen 855. In this sense, the dual balloonconfiguration is robust with respect to balloon integrity failure, inthat the failure of one balloon 860 is contained by the presence ofanother outer balloon 865.

Furthermore, the presence of the space 910 provides additional thermalinsulation which may be necessary when operating the device atrelatively low pressure inside of chamber 870. Empirical evidence showsthat at chamber static pressures of 15 psia, the cooling power of thecoolant flow expanding in the chamber 870 may at times be too high forsafe and effective cryotreatment of adjacent tissue. In order to operateat such pressures, additional thermal resistance is needed around theinner balloon 860 to mitigate the excessive cooling power of the device.The space 910 effectively provides such insulation, which may befine-tuned by applying varying levels of vacuum through the return lumen855. In such a manner, the effective temperature applied duringcryotreatment of tissue may be warmer than that of the boilingtemperature of the coolant.

However, FIG. 14 illustrates the disposition of the outer balloon 865around the inner balloon 860 such that an interstitial envelope or space910 exists therebetween, when inner balloon 860 is inflated to apressure higher than that present in the secondary vacuum return lumen855 and hence inside of the space 910. This may be the case prior to thecreation of vacuum pressure inside of the space 910, as applied throughthe secondary vacuum return lumen 855. However, once vacuum pressure isapplied into the space 910, the balloon configuration is that shown inFIG. 15. Under such conditions, the space 910 is effectively of zerodimension along the lateral faces L of both balloons, such that theinner balloon 860 and the outer balloon 865 are in contact with oneanother along length L.

If the space 910 is thereby closed, the containment and insulatingfunctions of the device are decreased. To counteract this, variousmethods and devices may be used to maintain the space 910 so as toenable vacuum containment of coolant leaks from, and provide additionalthermal resistance around, the chamber 870, while preventing the twoballoons 860 and 865 from sealing in and apposing against each other asshown in FIG. 15. The balloons 860 and 865 may still remain inapposition versus one another, but the space 910 will be maintained toachieve one of the purposes and functions of the present invention, asmore specifically explained below.

One such embodiment is shown in FIG. 16A, where the outer surface ofinner balloon 860 is modified to create small surface patterns thatextend from the outer surface as shown. As used herein, the term“surface modification” shall mean the creation or use of elements whosesurfaces are topographically non-uniform, i.e., non-smooth. The slope atany point on such a surface may be continuous or non-continuous, but thesurface itself will be continuous. These surface modifications 1010 maybe achieved through conventional plasma treatment, vapor deposition, orthrough the use of electrically conductive or radiopaque materials as isknown in the art, and may be patterned or non-patterned, so as to allowfor more effective fluid pathways through the space 910. Such surfacemodification thereby effectively maintains the space 910 at a finitelevel while vacuum is applied through the return lumen 855.

Other configurations which maintain the space 910 are shown in FIGS. 16Bthrough 16E. FIG. 16B shows the use of small particles 1020, such astalcum powder, to be lodged in the space 910. Alternatively, the space910 could be filled with a fluid, which may itself be radiopaque orelectrically conductive. In either case, the use of a vacuum returnlumen coupled to the outer balloon 865 is not needed, and the outerballoon 865 is sealed to the coaxial vacuum return tube 845 which alsoserves as the outermost tube of the catheter shaft. This allows theparticles 1020, or fluid if fluid is used, to be sealed and contained inthe space 1020 during operation of the device. Alternatively, a vacuumreturn tube such as is used in previous discussed embodiments may becoupled to the proximal end of balloon 865 and coupled with a separateinjection mechanism (not shown) for maintaining the steady flow andpresence of particles 1020, or fluid, as needed, so as to maintain space910 in its desired dimension.

FIG. 16C shows the use of regular or irregularly patterned surfaceridges 1030 coupled to either of: (i) the outer surface of inner balloon860, or (ii) the inner surface of outer balloon 865. Another alternativeto maintain space 910 is to use a braid or mesh type structure 1040 asshown in FIG. 16D, wherein the mesh 1040 surrounds the outer surface ofthe inner balloon 860. The cross-sectional thickness of the mesh 1040provides for the thickness of the space 910. The mesh 1040 may be abraid formed by a first group of flexible elongate elements 1042helically wound in a first direction of rotation and a second group offlexible elements 1044 helically wound in a second direction of rotationto create a braid as shown in FIG. 16D. The space 910 is thus maintainedby the apposition of each of the inner balloon 860 and the outer balloon865 against the mesh 1040, wherein each flexible elongate element has acircular cross section defined by a diameter. In an exemplaryembodiment, this diameter is in a range of approximately 0.001 to 0.010inches. The flexible elongate elements 1042 and 1044 may be formed ofmetal, or a filament or fiber such as nylon, aramid, or polyester.

Finally, another embodiment uses a coil 1050 as shown in FIG. 16E.Either of the coil or mesh may be made of metal, nylon, polyimide orother suitable material, as is known in the art. The coil 1050 mayinclude a single element wound in a direction around the inner balloon860, or may be formed by a number of such elements wound in a parallelrotational direction so as to form a coil or spring. Each such coilelement 1050 has a circular cross section defined by a diameter,wherein, in an exemplary embodiment, the diameter is in a range ofapproximately 0.001 to 0.010 inches. Alternatively, the coil element1050 may have a rectangular cross section defined by a height vs. awidth, wherein, in an exemplary embodiment, the height is in a range ofapproximately 0.001 to 0.010 inches, and the width is in a range ofapproximately 0.001 to 0.010 inches. The coil element 1050 may be formedof metal, or a filament or fiber such as nylon, aramid, or polyester.

The pressure conditions inside of the chamber 870 may also be monitoredand regulated through the use of a pressure transducer 1060 locatedinside of the chamber 870, as shown in FIG. 17. The pressure transducer1060 gives a user feedback control of the flow and pressure inside ofthe inner balloon 860 as the balloon is inflated and the catheter deviceis inserted and operated inside of a body lumen. Furthermore, theprimary vacuum return lumen 850 may be set with a back pressureeffective for inflating the cooling chamber 870 with the cooling fluidsuch that the cooling chamber 870 expands within a body lumen or vesselto position the device proximate to the vessel wall for performingcryotreatment. The back pressure is set to adjust the boilingtemperature of the coolant and thereby determine the temperature appliedto the surrounding tissue for cryotreatment. Such back pressure may bemonitored and controlled by means of additional pressure transducers(not shown) in the catheter body. Furthermore, such a back pressure maybe created by restricting the coolant return path through primary vacuumreturn lumen 850. Such restriction may be created by selecting adiameter of either of the injection tube 830, or coaxial return tube845, such that the coolant flow generates a residual pressure.Alternatively, the pressure conditions, including the chamber 870pressure and the back pressure in return lumen 850, may be regulated bythe control of the coolant fluid flow rates.

In addition to the embodiments discussed above, one or more sensors (notshown) may be disposed between the inner balloon 860 and the outerballoon 865. The sensors may further be disposed in the secondary vacuumreturn lumen 855, such as in a distal end portion of the lumen 855,proximate the two balloons. The sensors may be coupled to an externalcontrol unit or console which could also supply coolant to the catheter.When a leak develops in either the inner balloon 860 or the outerballoon 865, the sensors may detect such a leak and/or the flow of fluidand send a signal to the control console to interrupt or shut downcoolant flow to the catheter, or to otherwise alter the operation of theoverall catheter device and system. The sensor may be integrated with aflow control system operated through an external controller or console.When it sees any flow, it shuts off the coolant injection as a safetyfeature. The system may be automatic or subject to user input orcontrol. The system may be operated through an external console or viaan interface integrated with the catheter assembly itself.

In another embodiment of the present invention, as shown in FIGS. 13-14,the catheter 800 includes a proximal end portion and a distal endportion. The proximal end portion defines a fluid inlet port 825 and afluid outlet port 840. The catheter 800 may be incorporated in acatheter system which includes a coolant supply coupled to the fluidinlet port 825 and a source of vacuum coupled to the fluid outlet port840. A first expandable membrane 860 and a second expandable membrane865 are disposed on the distal end portion of the catheter 800, wherethe first expandable membrane 865 is expandable to define a coolingchamber 870. The second expandable membrane 865 is disposed around thefirst expandable membrane 860 to define an interstitial space 910therebetween.

A coolant injection lumen 835 is disposed in the catheter 800 in fluidcommunication with the fluid inlet port 825 and the cooling chamber 870.Thus, coolant injection lumen 835 fluidly connects the fluid inlet port825 and the cooling chamber 870. As used herein, the term “fluidlyconnect” shall mean the arrangement of one element in relation to twoother elements such that fluid may flow between the two other elementsthrough the one element. A primary coolant return lumen 850 is disposedin the catheter 800 in fluid communication with, and thereby fluidlyconnects, the fluid outlet port 840 and the cooling chamber 870. In thismanner, the coolant injection lumen 835, the cooling chamber 870, andthe primary coolant return lumen 850 define a first fluid pathway forthe flow of coolant.

A secondary coolant return lumen 855 is disposed in the catheter 800 influid communication with, and thereby fluidly connects, the fluid outletport 840 and the interstitial space 910. In this manner, theinterstitial space 910 and the secondary coolant return lumen 840 definea second fluid pathway for the flow of coolant, although no coolant ispumped into this second pathway. The second pathway only captures flowthat may leak from the first pathway or may enter the catheter from theoutside environment. The second pathway is “isolated” from the firstpathway in that no fluid may flow within the catheter between the firstand second pathways, unless a leak or an opening develops in any of thestructures separating the two pathways.

Finally, at least one sensor may be disposed anywhere inside or alongthe second fluid pathway, or may be included in the catheter 800 so asto be in fluid communication with the second fluid pathway. The sensormay be disposed inside or along the interstitial space 910 or in theouter return lumen 855.

The sensor may be a pressure sensor or a temperature sensor. Either ofthe pressure or temperature sensors may be an optical sensor, such asthose described herein.

By way of non-limiting example, the temperature sensor may include oneor more of a thermistor, a resistance temperature detector, athermocouple, or a solid state (semiconductor temperature sensor). Thethermistor may include a temperature-sensitive resistor having anegative temperature coefficient (NTC), wherein the resistance goes upas temperature goes down. The resistance temperature detector (RTD) mayinclude a wire that changes resistance with temperature. Typical RTDmaterials include copper, platinum, nickel, and nickel/iron alloy. AnRTD element can be a wire or a film, and may be plated or sprayed onto asubstrate such as ceramic. A thermocouple is a junction of twodissimilar metals, which produces a voltage when heated. An example of asemiconductor temperature sensor includes a PN junction, such as asignal diode or the base-emitter junction of a transistor. In oneembodiment, if the current through a forward-biased silicon PN junctionis held constant, the forward drop would decrease by about 1.8 mV perdegree C.

The sensor may also be an optical sensor. The optical sensor may be madeusing a photolithography process to create a silicon membrane on thesensor head, which reflects light proportional to pressure or canmeasure changes in reflectance off of metal diaphragms. Another methodfor an optical sensor is to use a Fabry-Perot interferometer to measurestrain, force and load, temperature, pressure, linear position and/ordisplacement. A broadband white light source may be conveyed via anoptical fiber to two mirrors, representing a strain gauge. As strain, inthe form of mechanical strain, heat strain, or other forces, is placedon the gauge, the distances between the mirrors change and modulate ameasured optical spectrum. The return signal passes through an opticalcorrelator before reaching a linear CCD array. By detecting the maximumsignal strength on the linear array, the system determines the absolutedistance between the mirrors and therefore the strain inside thestructure. This strain can be related to pressure or temperature, andhence, to the flow conditions inside the catheter 800.

Another embodiment, by way of non-limiting example, is to use fiberoptics in an optical sensor with microbend fibers. The main applicationfor microbend fibers, however, is strain analysis. As strain on thefiber stretches the fiber, the result is a marked change in lighttransmission. By encapsulating the fiber in a hypodermic-shaped metaltube that expands with heat, the microbend fiber can also measuretemperature fluctuations.

Another embodiment for of the sensor is a “flow switch.” As used herein,the term “flow switch” shall mean a device that incorporates twoopposing magnets positioned in close proximity. One magnet is fixed andthe other is movable, but held apart by the magnetic force. When a fluidflows past the magnets, at a given flow the force is sufficient toovercome the opposing magnetic force and it pushes the magnets together.This closes the circuit and “trips” the switch. The flow switch isgenerally either an “on” or “off” signal. The same effect could beachieved by using a flow meter to measure the gas flow through a lineand at a given set point trigger the “failure.” Thus, the sensors incatheter 800 may include a flow switch, a flow meter, or both elements.In one embodiment of the present invention, the flow switch includes afirst magnet fixed to the catheter. A second magnet is disposedproximate the first magnet, the second magnet being held at asubstantially fixed position displaced from the first magnet by themagnetic force between the first and second magnets. A detection circuitis coupled to the flow switch to determine when the magnets are nolonger separated. The circuit may be coupled to an external controlleror console which controls the flow of coolant through the system.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

1. A catheter leak detection system, comprising: a catheter havingproximal and distal end portions, the proximal end portion defining atleast one fluid outlet port coupled to a vacuum source; an expandablecooling chamber disposed on the distal end portion; an expandablemembrane disposed around the cooling chamber to define an interstitialspace therebetween; a primary coolant return lumen fluidly connectingthe at least one fluid outlet port and the cooling chamber; a secondarycoolant return lumen fluidly connected to the interstitial space; and atleast one sensor detecting the flow of fluid in the fluid pathway. 2.The catheter leak detection system of claim 1, wherein the at least onesensor detects a leak of fluid from the cooling chamber to the fluidpathway.
 3. The catheter leak detection system of claim 1, wherein theat least one sensor detects a leak of fluid through the expandablemembrane.
 4. The catheter leak detection system of claim 1, wherein theat least one sensor includes a pressure sensor.
 5. The catheter leakdetection system of claim 1, wherein the at least one sensor includes anoptical sensor.
 6. The catheter leak detection system of claim 5,wherein the optical sensor includes a Fabry-Perot interferometer.
 7. Thecatheter leak detection system of claim 5, wherein the optical sensorincludes microbend fibers.
 8. The catheter leak detection system ofclaim 1, wherein the at least one sensor includes a temperature sensor.9. The catheter leak detection system of claim 1, wherein the at leastone sensor includes a flow switch.
 10. The catheter leak detectionsystem of claim 9, wherein the flow switch includes: a first magnetfixed to the catheter; a second magnet disposed proximate the firstmagnet, the second magnet being held at a substantially fixed positiondisplaced from the first magnet by the magnetic force between the firstand second magnets; and, a detection circuit coupled to the flow switch.11. The catheter leak detection system of claim 1, wherein the at leastone sensor includes a flow meter.
 12. The catheter leak detection systemof claim 1, further comprising a coolant supply in fluid communicationwith the cooling chamber.
 13. The catheter leak detection system ofclaim 1, wherein the secondary coolant return lumen is isolated from thecooling chamber.
 14. The catheter leak detection system of claim 1,wherein the secondary coolant return lumen is in fluid communicationwith the primary coolant return lumen at the proximal end portion. 15.The catheter leak detection system of claim 1, wherein the primary andsecondary coolant return lumens are coaxial.